In many contexts one may desire to scan images in order to form an electric signal. The signal can be used for long-distance transmission of the images, for presentation using media such as electronic displays and for use in electrotyping, to name just a few possibilities.
The image often consists of a photographic picture. Because of the limited exposure latitude of the photographic film, that is to say, its ability to correctly render a wide range of illumination intensity, photographic images of subjects with greatly varying illumination intensity are rendered in such a way that dark shadows and brightly iluminated sections become, respectively, too dark or too light even when the exposure setting is correct for certain other sections.
When enlarging a negative material onto a light-sensitive positive material it is possible to correct unevenness in the exposure by shading certain sections such that during a portion of the exposure time one holds a shading object in the light path from the thinnest sections of the negative. One moves the object, which can be a hand or some suitably cut piece of paper, so that sharp contours will not be formed on the enlargement.
In order to achieve a corresponding correction ability it is previously known that, during electronic processing of images, the produced signal may be used to generate an electronic representation of the image on a display, such as a cathode ray tube (CRT). In this way one may determine whether the brightness of a particular section needs to be increased or decreased in order to bring out the details even in the dark shadows or to prevent the brightest sections from being washed out. It is previously known that one may utilize a light pen, for example, with which one may ring in one the display the regions which are to be corrected and give a suitable manoeuvre signal for this correction. However, this method for correcting the degree of illumination of the images gives rise to delimited fields where the corrections have been made which do not run together smoothly with the rest of the picture. Said known method of correcting images which have been scanned in order to produce an electric signal does not therefore give a satisfactory result.
It is an object of the present invention to provide a device for correction of images which are represented in the form of an electric signal so that a better image representation than the original is achieved for dark or light sections, without discernible transitions between corrected and uncorrected sections.